Completed oil wells have piping and a valve assembly installed on the top of the well casing. This valve assembly is often called an oil well head (or tree) in oil field jargon. The configuration of this well head can vary from well to well. These well heads are often protected by well houses. A typical well house is a small building, approximately 20 feet square. The well house provides a sheltered environment for the well head and permits work crews to maintain the well heads in relative comfort. Installed within the floor, and surrounding the well head, is a cellar. The cellar is used during the drilling phase of the well development. This cellar typically has a metal grate installed over it to provide a level work surface. With today's environmental regulations, oil, hydraulic fluid, drilling mud and other contaminants are no longer permitted to be spilled into the cellar. This means that whenever a well head needs service, care must be taken to catch and collect any spilled contaminants that may escape from the piping.
A few devices have been developed to collect spilled products from well casings. One example, U.S. Pat. No. 4,673,034 to Hansen, discloses a flexible pad that is designed to funnel liquids away from the casing of water wells. This device is used to stop runoff that percolates down around a casing, which may contaminate the well water. The device has a ring that is fastened to the casing using a hose clamp. The ring is attached to a circular skirt that is sloped down and away from the well casing. This design, therefore, is designed to move liquid away from the casing. It also has no provision to catch or contain the runoff.
Two patents that are useful in collecting oil or other liquids are found in U.S. Pat. Nos. 5,098,220 to Norman and 5,101,868 to Balch. The Norman Patent is designed to cover and protect a shallow pit by placing an impermeable membrane into the bottom of the pit. It is a large sheet of material with a circular hole in the center. The sheet is split to the center to permit it to be spread it around a well casing and then close it to secure it for use. A special collar is provided to provide a leak-proof seam around the casing. The unit is sealed in place by a second sheet that is one-half the size of the lower sheet. This sheet has no seams and is designed to be glued over the seam of the lower sheet. In this way, a permanent liner for the pit is created. Although this device is adequate for a permanent pit liner, it is not designed for temporary use. The top sheet is glued to the lower sheet to ensure a good seal. Once glued in place, the mat cannot be removed unless it is cut.
The Balch patent teaches a design for catching spills involving fill pipes. Here, the device is a funnel-shaped basket that is fastened to a pipe with liquid-tight fasteners. The basket catches any spilled liquid from the pipe. Although this device works well on narrow diameter pipes, it does not appear readily convertible for use over a typical well head, which has large valves and other appurtenances and is not uniform in shape. Also, the technique of using elastic bands to form a liquid tight seal, as taught by Balch, is impractical where the shapes of the objects to be sealed are nonuniform.